Understanding Recovery Is as Important as Understanding Decline: The Case of the Crested Ibis in China

Abstract

The wild population of the crested ibis (Nipponia nippon) has recovered remarkably from seven individuals in 1981 to over 7000 in 2021. However, it is unclear how key factors, from endogenous density dependence to exogenous environmental pressure, have contributed to the species’ recovery. We used species distribution models to quantify the contributions of climatic variables, human impact, land form and land use in order to understand the recovery process in the context of prevailing environmental conditions. We also calculated the nest density over the past 39 years to estimate the influence of density dependence on population dynamics. We found that the interaction between rice paddy areas and water bodies (rivers, lakes and ponds) had the highest contribution to nest site selection, whereas linear terms for either rice paddies or water bodies alone had little effect. During its recovery, sub-populations in two watersheds have been constrained by high density and have experienced logistic growth, while other sub-populations in over seven watersheds are growing exponentially. Our models indicate that exogenous environmental factors are more important than density restriction at this stage. In China’s transformed landscape, the crested ibis needs both rice paddies and water bodies to fulfil its annual life cycle. Habitat protection should thus cover both habitat types to ensure the long-term survival of this still endangered species.